1. Field of the Invention
The present invention relates to a determination apparatus for determining the type of a recording medium and to an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses determine the types of recording media, and set image forming conditions (transfer condition, fixing condition, etc.) in accordance with the type of the recording medium. Japanese Patent Laid-Open No. 2010-18433 proposes to irradiate a recording medium with an ultrasonic wave and detect the transmission coefficient of the ultrasonic wave that is transmitted by the recording medium so as to determine the grammage (weight per unit area) of the recording medium.
Incidentally, ultrasonic wave sensors are provided with a transmission part and a reception part, and the transmission part and the reception part are each constituted by a piezoelectric element. The terminals of the piezoelectric element have positive and negative polar characters. Whether or not the polar characters of the piezoelectric element of the transmission part and the polar characters of the piezoelectric element of the reception part match influences the determination result of a recording medium.
However, managing polar characters increases component costs and assembly costs. Moreover, managing polar characters is not required due to the use of ultrasonic waves. Therefore, many ultrasonic wave sensors serving as general purpose components whose polar characters are not managed exist in the market. Accordingly, if the type of the recording medium can be determined using the general purpose components in which the polar characters of the transmission part and the reception part are not managed, it will be possible to reduce the cost of a determination apparatus.